GENERAL

In two dimensional experiments resolution in the indirect dimension is usually limited.  The default spectral width settings for many experiments are therefore more restrictive and may not include chemical shift regions towards the edge of the range. For example aldehyde carbons may not be included in the default HSQC experiments.

MANUALY SETTING WINDOW

If you are running automation, you can check and modify parameters by using the “Modify Parameters” button in the experiment setup line .

This will bring up the parameters window:

The parameters to change the spectral window (highlighted) are 2SW and O1P for the direct dimension (typically proton), 1SW and O2P for the indirect dimension (can be c13, n15 etc). For COSY, set 1SW equal 2SW, and don’t set an O2p.

To translate a given sw and o1p to spectral limits, use

• leftlimit = o1p + sw/2
• rightlimit = o1p – sw/2

For a window from leftlimit to rightlimit one needs to set

• sw = leftlimit – rightlimit
• o1p = rightlimit + sw/2

For example, for a 10-190ppm window, sw=180ppm and o1p=100ppm.

INCREASE SIGNAL TO NOISE OR RESOLUTION

To adjust experiment time, increase 1td (number of individual spectra) for better resolution and signal to noise, or ns (number of scans per individual spectrum) for better signal to noise only (circled in red)

AUTOMATED DETECTION OF SPECTRAL WINDOW

Optimization of spectral window can be done automatically by the Topspin software.  If you run unknown samples in automation, that can be useful.

In IconNMR, several composite experiments are available that automatically optimize the sweep width using 1D experiments.  They are showing at the bottom of the list and are prepended with a “C”:

C h1-cosy – {H1 and sweep width optimized COSY}
C h1-hsqc – {H1,f2 Sweep width optimized HSQC}
C h1-c13-hsqc – {H1,c13, f1/f2 Sweep width optimized HSQC)
C H1-dept-hsqc (H1, C-13-DEPT135, f1/f2 sweep width optimized HSQC}
C c13-cosy-hsqc – {Proton, C13, HSQC and COSY}
C hsqc-cosy-hmbc – {Proton, C13, HSQC, COSY and HMBC spectra}

The experiments will create 1D experiments, and then run the 2D experiments with the spectral widths optimized for the region of the 1D experiments containing signals. This should usually ensure that no signals are left out in the 2D experiment, but strong solvent signals can cause weak compound signals to be missed..

Use of the DEPT for setting up the HSQC should only optimize for protonated carbon signals.